1. Field of the Invention
This invention relates to a legged mobile robot, more particularly to a legged mobile robot equipped with a mechanism for absorbing and moderating impacts produced by external forces during footfall or the like, or a foot structure for enhancing the ground gripping force, or a locomotion control system of the robot equipped with the structure.
2. Description of the Prior Art
Wheeled, crawler, legged or other types of mobile robots have been proposed. Among the numerous reports published regarding control technologies for the legged robot are (Raibert, M. H., Brown, Jr. H. B., "Experiments in Balance with a 2D One-Legged Hopping Machine", ASME, J of DSMC, vol. 106, pp. 75-81 (1984)), the two-legged robot (J of the Robotic Society of Japan, vol.1, no. 3, pp. 167-203 (1983)), the four-legged robot (J of the Robotic society of Japan, vol. 9, no.5, pp. 638-648 (1991)), and the six-legged robot (Fischeti, M. A., "Robots Do the Dirty Work", IEEE, Spectrum, vol. 22, no.4, pp. 65-72 (1985) and Shin-Min Song, Kenneth J. Waldron, "Machines That Walk; The Adaptive Suspension Vehicle", The MIT Press Cambridge, Mass., London, England). Other reports have been published regarding techniques for real time generation of a dynamically stable motion (walking) pattern for a robot which relatively few degrees of freedom (Shimoyama, "Dynamic Walking of Stilt-type Biped Walking Robot", Collected Papers of The Japan Society of Mechanical Engineers, book C, vol.48, no. 1445-1454 (1982) and "Legged Robots on Rough Terrain; Experiments in Adjusting Step Length", by Jessica Hodgins, IEEE (1988)), and also on techniques for offline generation of a stable motion (walking) pattern for a robot with relatively many degrees of freedom (Japanese Laid-Open Patent Publication nos. 62(1987)-97006 and 63(1988)-150176). Also the assignee proposed the anthropoid biped robot in Japanese Laid-open Patent Publication No. 3(1991)-184,782.
Among robots, the biped type constantly receives a force of reaction from the ground on the foot or feet in contact with the ground. In particular, at the time the free leg touches down during walking, the reactive force may become an impact of such magnitude that it disturbs the robot's attitude and causes it to become unstable. The legged mobile robot proposed earlier by the assignee comprises links interconnected by joints which are driven by motors through reduction gear mechanism made up of Harmonic drives (trade name) so as to vary the relative positions among the links. The impacts produced at footfall act as loads on the reduction gear mechanisms, bearings and other parts of the joint drive mechanism. In addition, since the legged mobile robot walks by alternately swinging first one and then the other of its two legs forward, the swinging force (inertial force) produced at the time the free leg is thrown forward acts as a load on the free leg joints, particularly on the knee joints. Such loads produced by external forces have an adverse effect on the service life of the joint drive mechanisms and are also a cause of robot's attitude instability. These footfall impact forces and inertial forces may further have an adverse effect on the robot's onboard control unit, which uses a microcomputer and other precision electronic components, as well as on any payload the robot may be carrying.